---
# (DD10) Business Logic — NumericFilter.isValid() [17 LOC]

| Field | Value |
|-------|-------|
| Fully Qualified Name | `com.github.blaxk3.ui.NumericFilter` |
| Layer | Utility |
| Module | `ui` (Package: `com.github.blaxk3.ui`) |

## 1. Role

### NumericFilter.isValid()

This method enforces a lightweight numeric-format validation rule for UI input. It accepts an empty string as valid, which indicates that the surrounding screen logic allows blank input as a permissible state rather than forcing a value at this stage. For non-empty input, it verifies that the text contains only digits, with one special exception: a single decimal point is allowed, and it may appear anywhere as long as it does not occur more than once. This makes the method suitable for reusable client-side filtering of numeric fields where decimal values may be entered by a user.

In business terms, the method acts as a shared input gate for numeric entry rather than a persistence or service operation. It implements a simple validation-and-routing pattern: empty values are passed through, decimal numbers are conditionally accepted, and any other non-digit character causes immediate rejection. Within the larger system, this is a UI-level utility that helps prevent invalid keystrokes or pasted text from reaching downstream processing.

## 2. Processing Pattern (Detailed Business Logic)

```mermaid
flowchart TD
    START(["isValid(text)"])
    DECISION1{"text is empty"}
    RETURN_TRUE1["Return true"]
    INIT_DECIMAL["Initialize decimalCount = 0"]
    INIT_LOOP["For each character in text"]
    GET_CHAR["Read current character ch"]
    DECISION2{"ch == '.' and decimalCount != 1"}
    INC_DECIMAL["Increment decimalCount"]
    DECISION3{"Character.isDigit(ch)"}
    RETURN_FALSE["Return false"]
    RETURN_TRUE2["Return true"]
    START --> DECISION1
    DECISION1 -- "Yes" --> RETURN_TRUE1
    DECISION1 -- "No" --> INIT_DECIMAL
    INIT_DECIMAL --> INIT_LOOP
    INIT_LOOP --> GET_CHAR
    GET_CHAR --> DECISION2
    DECISION2 -- "Yes" --> INC_DECIMAL
    DECISION2 -- "No" --> DECISION3
    INC_DECIMAL --> INIT_LOOP
    DECISION3 -- "Yes" --> INIT_LOOP
    DECISION3 -- "No" --> RETURN_FALSE
    INIT_LOOP --> RETURN_TRUE2
```

## 3. Parameter Analysis

| No | Parameter Name | Type | Business Description |
|----|---------------|------|---------------------|
| 1 | `text` | `String` | The candidate user-entered value being evaluated by the numeric input filter. It may be blank, a whole number, or a decimal number with a single period. If it is empty, the method accepts it as valid. If it contains any non-digit character other than one decimal point, the method rejects it. |

**Instance fields / external state read:** None. The method depends only on the `text` argument and local variables.

## 4. CRUD Operations / Called Services

The method does not invoke any business service, persistence, or CRUD endpoint. Its only work is local validation of the input string.

| CRUD | SC / CBS | SC Code | Entity / DB | Operation Description |
|------|----------|---------|-------------|-----------------------|
| - | - | - | - | No external service or database access. Local character-by-character validation only. |

## 5. Dependency Trace

### Pre-computed evidence from code analysis graph:

No screen/batch entry points found within 8 hops. Direct callers found: 0 methods.
Terminal operations from this method: -

This method is a leaf-level utility with no downstream business service calls. The only observable dependency is that other code in the same `UI.java` file may reuse it as a validation helper for numeric text fields.

| # | Caller (Screen/Batch) | Call Chain (Full Path to this Method) | Terminal (SC / CRUD / Entity) |
|---|----------------------|--------------------------------------|-------------------------------|
| - | - | - | - |

## 6. Per-Branch Detail Blocks

**Block 1** — IF `(text.isEmpty())` (L196)

> Accepts blank input as valid, allowing optional numeric fields to remain empty.

| # | Type | Code |
|---|------|------|
| 1 | RETURN | `return true;` |

**Block 2** — ELSE (L199-L206)

> Validates each character of the input one by one. A single decimal point is allowed; all other characters must be digits.

| # | Type | Code |
|---|------|------|
| 1 | SET | `byte decimalCount = 0;` |
| 2 | EXEC | `text.length()` // determine loop boundary |
| 3 | EXEC | `text.charAt(i)` // read the current character |
| 4 | IF | `if (ch == '.' && decimalCount != 1)` |
| 5 | SET | `decimalCount++;` |
| 6 | ELSE-IF | `else if (!Character.isDigit(ch))` |
| 7 | RETURN | `return false;` |
| 8 | LOOP-END | `for (int i = 0; i < text.length(); i++)` continues until all characters are checked |

**Block 3** — RETURN (L208)

> Reaches the success path only when every character is acceptable under the numeric-format rule.

| # | Type | Code |
|---|------|------|
| 1 | RETURN | `return true;` |

## 7. Glossary

| Term | Type | Business Meaning |
|------|------|------------------|
| `text` | Field/Parameter | User-entered value being checked for numeric format compliance. |
| decimal point (`.`) | Symbol | Separates integer and fractional parts in a decimal number. |
| `Character.isDigit` | Technical API | Java standard library check that confirms whether a character is a numeric digit. |
| numeric filter | Business term | UI validation rule that allows only numeric text patterns to be entered. |
| blank input | Business term | An empty field value that is treated as acceptable by this method. |
| decimal number | Business term | A number that may include a fractional component separated by one period. |
| `decimalCount` | Local variable | Internal counter used to ensure that at most one decimal point is present. |